The present invention relates to a metal diaphragm valve, and more particularly, to a metal diaphragm valve adapted for use in pipe arrangements through which fluids of very high purity flow.
In such fields as the manufacture of semiconductors, fluids of very high purity are required. Valves incorporated in pipe arrangements for circulating such fluids must fulfill the following special requirements:
First, no impurities should be generated within the valves. Secondly, when a fluid circulating through the circuits is replaced with another one, none of the replaced fluid should remain in the valves. In other words, it should be relatively simple to remove replaced fluid from the valves.
Bellows seal valves are generally used in such pipe arrangements, and the purity of the fluid in fluid circuits having these valves therein is 1 ppm or thereabout. In place of the bellows valves, diaphragm valves have started to be used as valves adapted for fluids of higher purity. In general, a metal diaphragm valve comprises a flexible metal diaphragm which serves to isolate a valve chamber from the outside, the chamber containing a valve seat and a valve disk. With the aid of the diaphragm, drive means is used to drive the valve disk, to open or close the valve. In a conventional metal diaphragm valve incorporated is such pipe arrangements, a drive means is arranged outside a valve chamber, while a valve disk and a return means for restoring the valve disk, such as a return spring, are housed inside the chamber. The drive means is used to drive the valve disk with the aid of a metal diaphragm, and the return spring serves to restore the disk and the metal diaphragm to their original positions. In the case of the metal diaphragm valves constructed in this manner, since the valve chamber must receive the return means, this results in the chamber having so large a capacity, and replaced fluids cannot be expurgated readily therefrom. During actual operation, moreover, the valve disk and the return spring, or the disk and a valve seat, slide against each other, giving rise to the danger that metallic dust and other impurities will be produced. In another metal diaphragm valve of conventional type, an upper stem, which is driven directly by drive means, and a lower stem, which is coupled to a valve disk, are connected together through a metal diaphragm. The valve disk, which is housed within a valve chamber, is driven by the drive means and return means, arranged outside the chamber, through the medium of the upper and lower stems. In this way, the valve is opened or closed. With this arrangement, therefore, there is no return spring inside the valve chamber. In this diaphragm valve, however, the diaphragm must be formed with through-hole, to facilitate the connection between the upper and lower stems. Provision of the hole. unfortunately, entails a problem in that it is possible the fluid may then leak to the outside or become mixed with external foreign matter introduced therethrough. This problem becomes all the more serious with an increase in the frequency of valve operation. In this diaphragm valve, moreover, the valve chamber, which is expected to be able to house the lower stem therein, has so large a capacity that the fluid replacing capability of the valve is poor.
Processes of manufacturing VLSIs, for example, require use of fluids of higher purity or of the ppb-order level. Having the aforementioned problems, the conventional diaphragm valves cannot be suitably used to handle fluids of purity of the ppb order or higher level, which will possibly be needed in the future.